Zeinab Kalantari

Department of Physics, Sharif University of Technology,

Research Center for High Energy Physics, Department of Physics, Sharif University of Technology

A Study of Cosmological Models Based on Long Gamma-ray Bursts Duration Histogram

Abstract: In this presentation, I want to speak about the idea of constraining the cosmological model by the long GRBs’ duration data of the Swift-BAT satellite. Gamma-ray bursts’ powerful luminosity enables us to explore the universe at the farthest redshift reaches ever explored. The maximum observable redshift of gamma-ray bursts is estimated to be around $z=9.4$, so GRBs could serve as an excellent tool to investigate the characteristics of the cosmos at high redshifts, such as constraining the cosmological parameters such as dark energy equation of state. The burst duration $T_{90}$ is a significant property of GRBs that can be analyzed. In my presentation, I focus on comparing the histogram of long GRBs’ duration resulting from a kind of $ \omega CDM$ cosmological model with an energy equation of state, $P= c \omega(z) \rho$ and a $\Lambda CDM$ model. I considered a cosmological model for $\omega(z)=-1 +\alpha z$ then I tried to find the best $\alpha$. In this paper, we first calculate the detection rate of Swift/BAT for a cosmological model with the $ \omega CDM$ model. We use this probability density function to generate the redshift of LGRBs in our Monte-Carlo simulation. in a Monte Carlo simulation, we want to simulate $\tau = \tau_0 (1+z)$ for 1347 mock LGRBs and compare the histogram of $\tau$ for assumed cosmological model and observational histogram of $\tau$. Finally, $\chi^2$ minimization method is employed to determine the optimal value of $\alpha$ in the dark energy equation of state, $P= c \omega(z) \rho$, with $\omega(z)=-1+\alpha z$ . We showed that for the $\omega CDM$ model all values of $\alpha$ within $\alpha=[0, 0.16]$ range are considered acceptable within two standard deviations.

یکشنبه  16 دی 1403، ساعت 17:00

Sunday 5 January 2025 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3 /  

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Arefeh Alizadeh

Department of Physics, Sharif University of Technology

Dark Matter Phenomenology: Production Mechanisms and Freeze-In via Inverse Semi-Annihilation

 Abstract: Dark matter is a key part of modern cosmology and particle physics. Studying its evolution and properties helps us understand the universe’s large-scale structure, galaxy dynamics, and the fundamental particles that may exist beyond the Standard Model.

In this presentation, I will give an overview of the evidence supporting the existence of dark matter and the possible candidates proposed to explain these observations. Production mechanisms, including misalignment, thermal freeze-out, and freeze-in, will be discussed. I will then focus on the freeze-in mechanism, a well-motivated scenario for non-thermal dark matter production. As discussed in arXiv:2104.05684, through inverse semi-annihilation processes, the freeze-in mechanism can explain the current abundance of dark matter. The semi-production approach allows for larger coupling values compared to the usual freeze-in scenario by considering a small initial abundance of dark matter.

یکشنبه 9 دی 1403، ساعت 17:00

Sunday 29 December 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Adeela Afzal

Department of Physics, Quaid-i-Azam University, Islamabad, Pakistan

Tracing the Cosmos with Stochastic Gravitational-Wave Background

Abstract: Hybrid inflation provides a rich framework for understanding the early universe’s dynamics and its connection to observable cosmic structures. This talk will explore the role of hybrid inflation in generating topological defects and the stochastic gravitational wave background, emphasizing model-building approaches to connect theoretical predictions with observations. I will discuss the potential origins of the signals detected in the NANOGrav 15-year dataset and how they relate to cosmic phenomena such as scalar-induced gravitational waves and cosmic strings. Furthermore, we will delve into the intriguing possibility of primordial black hole formation during hybrid inflation and its implications for current and future astrophysical observations.  I will also talk about weighted Morphology and its implications on topological defects. This presentation aims to bridge theoretical insights with observational data, shedding light on the intricate interplay between inflationary physics, gravitational waves, and primordial black holes.

یکشنبه 18 آذر 1403، ساعت 17:00

Sunday 8 December 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3 /  

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Mahdiyar Mousavi-Sadr

School of Astronomy, Institute for Research in Fundamental Sciences (IPM)

 A statistical study of exoplanetary systems and the correlations between their parameters 

Abstract: The number of discovered exoplanets is increasing dramatically, so that over 5,500 exoplanets have been confirmed to date. This large number of exoplanets and advances in machine-learning techniques open new avenues for exploring and understanding the characteristics of worlds beyond our Solar system. In this study, we use machine learning approaches to analyze a data set comprising 770 planets, aiming to characterize their fundamental quantities. We classify the data into two main classes: ‘small’ and ‘giant’ planets. Furthermore, using different regression models, we try to uncover possible correlations between stellar and planetary parameters. Notably, our study reveals a noteworthy finding: there is a positive linear relation between the size of giant planets and the mass of their host stars, which might provide interesting insights into the formation and evolution theories of planets.

یکشنبه 11 آذر 1403، ساعت 17:00

Sunday 1 December 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Armin Sadeghi

Department of Physics, University of Tehran

Collapse into regular black holes 

Abstract: In this talk, we explore the formation of regular black holes with de Sitter cores, from the gravitational collapse of a massive star based on a generalized Oppenheimer–Snyder collapse model. The collapse scenario leads to a class of general regular black holes with de Sitter cores. We will examine key properties of these black holes, including their horizons, energy conditions, and surface gravity.

یکشنبه  4 آذر 1403، ساعت 17:00

Sunday 24 November 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Golshan Ejlali

School of Astronomy, Institute for Research in Fundamental Sciences (IPM)

 Investigating Millimeter Emission in Nearby Galaxies 

Abstract:D ust plays a crucial role in the interstellar medium of galaxies, influencing their thermal, chemical, and radiative properties. It absorbs and scatters starlight, leading to extinction and reddening effects, and re-emits the absorbed energy in the far-infrared. Dust also cools the interstellar medium by emitting radiation in infrared and submillimeter wavelengths and acts as a catalyst for molecular hydrogen formation, essential for star formation.  The IMEGIN project (Interpreting Millimeter Emission of Galaxies with IRAM and NIKA2) leverages the NIKA2 camera on the IRAM 30m telescope to explore millimeter properties of galaxies, focusing on dust emission beyond 500 µm to detect cold dust components. This project, led by Dr. Suzanne Madden and involving 14 European institutes in addition to IPM from Iran, aims to disentangle contributions from dust, synchrotron, and free-free emissions. High spatial resolution maps of these emissions will advance our understanding of star formation and dust evolution in galaxies. We utilized multi-wavelength data from Herschel, Spitzer, and Planck in infrared and submillimeter, and from VLA, Effelsberg and WSRT in radio regime to complement NIKA2 observations, constructing detailed spectral energy distributions (SEDs) for a diverse sample of galaxies. This enables the separation of different emission components and derivation of key physical parameters such as dust temperature, mass, and composition. We investigated the relationship between dust properties and galactic characteristics like star formation rate, and morphology, providing insights into dust evolution and galaxy evolution. We also suggest millimeter emission as a powerful extinction-free tracer of molecular gas across various galactic environments.

یکشنبه  27 آبان 1403، ساعت 17:00

Sunday 17 November 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Ali Rostami

Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan

Black Holes as Catalysts: The Far-Reaching Effects of Black Hole Retention in Evolution of Star Clusters 

Abstract: Massive stars, upon exhausting their thermonuclear fuel, undergo gravitational collapse followed by supernova explosions, leaving behind black holes (BHs) as remnants. These explosions aren’t perfectly symmetrical, and the uneven ejection of mass imparts a “natal kick” to the newborn BH. The magnitude of these kicks remains a subject of debate, creating uncertainty about the initial population of BHs retained in star clusters. High natal kicks lead to the immediate ejection of BHs from their host clusters, while gentler kicks allow them to stay put, forming a sub-system of BHs right in the cluster’s heart. This BH sub-system (BHSub) acts like a bustling, dynamic factory at the cluster’s core, pumping energy into its surroundings and dramatically influencing its evolutionary path.

In this talk, I’ll first address the dynamical processes governing clusters harboring a BHSub, followed by an examination of the emergence and evolution of the dark cluster phase. But that’s not all – I’ll demonstrate how assuming low natal kicks for BHs and the subsequent formation of a BHSub in the cluster’s heart can provide explanations for several outstanding open questions regarding globular clusters:

1. The origin of high dark remnant fractions in Milky Way globular clusters
2. The dichotomy between metal-rich and metal-poor globular clusters in the Milky Way
3. The mysterious lack of metal-poor globular clusters in the inner regions of early-type galaxies

By the end, you’ll see just how far-reaching the effects of BH retention can be in the grand story of star cluster evolution.

یکشنبه  20 آبان 1403، ساعت 17:00

Sunday 10 November 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Saeed Pourojaghi

Department of Physics, Bu-Ali Sina University, Hamedan.

Recent Challenges to the Standard Cosmological Model 

Abstract: The standard cosmological model (ΛCDM) is considered the first and simplest model to describe the accelerated expansion of the universe. Despite its good compatibility with observational data, this model faces various theoretical and observational challenges. In this talk, I intend to discuss the latest challenges to this model. First, we will examine the redshift evolution of the free parameters of the ΛCDM model using observational data binning. This approach is significant because these parameters are mathematically and observationally considered constants, but our results show different values for them in various redshift bins. In the next part of my talk, we will present a study on the cosmological constraints of dark energy parametrizations post-DESI 2024, suggesting potential deviations from the standard ΛCDM cosmology. Our main goal is to examine the results of DESI collaborations on some extensions of the CPL approximation, known as the BA and Pade parametrizations. Finally, we will provide an analysis of the ΛCDM model using a cosmography approach, which includes recent DESI BAO observations and Type Ia supernova catalogs, including the DES-SN5YR and Pantheon+ sets.

یکشنبه  13 آبان 1403، ساعت 17:00

Sunday 3 November 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 /Physics Department – first floor – Room Physics 3   

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Samaneh Sarbaz

Department of Physics, Sharif University of Technology

Frequency shift in binary microlensing 

Abstract: Gravitational microlensing with binary lensing is one of the channels for detecting exoplanets. Due to the degeneracy of the lens parameters for the binary microlensing, additional features such as parallax and finite-size effects need to identify the lens parameters. The frequency-shift effect as the relativistic analogy of the gravity assist for the photons, is an extra observation that provides additional constraint between the lens parameters. In this work, we extend the application of the frequency shift effect to binary microlensing and derive the frequency shift during the lensing and caustic crossing. The frequency shift for the binary lens is of the order of $\Delta\nu/\nu∼10^{-12}$. We also investigate the feasibility of detecting this effect by employing Cross-Correlation methods.

یکشنبه  6 آبان 1403، ساعت 17:00

Sunday 27 October 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Hedieh Abdollahi

School of Astronomy, Institute for Research in Fundamental Sciences (IPM)

The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies VIII, Detection of the Long Period Variable Stars of Andromeda Dwarf Satellite

Abstract: We present an extensive analysis of spheroidal dwarf satellite galaxies of the Andromeda galaxy, aiming to provide a comprehensive catalog of long-period variable (LPV) stars. This study is part of an optical monitoring survey targeting 55 dwarf galaxies and four globular clusters in the Local Group. Observations were conducted using the Wide Field Camera (WFC) on the 2.5-meter Isaac Newton Telescope (INT) over nine epochs, employing the i-band (Sloan) and V-band (Harris) filters. Our focus is on detecting asymptotic giant branch (AGB) stars with magnitude amplitudes exceeding 0.2 mag to trace the evolution of these dwarf galaxies. The resulting catalog of LPV candidates in Andromeda’s satellite galaxies provides updated characteristics such as half-light radii, TRGB magnitudes, and distance moduli. By applying the Sobel filter, we determine distance moduli for these satellites, ranging from 23.57±0.08 to 25.62±0.17 mag. Given that LPV stars in dwarf galaxies span ages from 30 Myr to 10 Gyr, they serve as valuable probes for reconstructing star formation histories (SFHs). The relationship between LPV birth mass and luminosity at the end of their evolution makes them ideal for studying galaxy properties. This catalog will also facilitate the estimation of quenching times, galaxy masses, and the assessment of mass-loss and dust production in these systems.

یکشنبه  29 مهر 1403، ساعت 17:00

Sunday 20 October 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest